CN110491755B

CN110491755B - Cathodoluminescent optical concentrator

Info

Publication number: CN110491755B
Application number: CN201910393019.XA
Authority: CN
Inventors: J·A·亨特; M·贝蒂尔松; T·沃斯利
Original assignee: Gatan Inc
Current assignee: Gatan Inc
Priority date: 2018-05-14
Filing date: 2019-05-13
Publication date: 2022-01-04
Anticipated expiration: 2039-05-13
Also published as: US10707051B2; JP6814247B2; EP3570311B1; JP2019200990A; US20190348257A1; CN110491755A; EP3570311A1

Abstract

An apparatus for collecting, distributing and analyzing Cathodoluminescence (CL) and other light signals in an electron microscope is provided. An optical hub utilizing a linearly translating fold mirror and mounted to an electron microscope is used to receive substantially collimated light collected from the collection mirror and efficiently route the collected light to a plurality of optical analysis instruments. The linearly translating fold mirror can provide fine positional alignment of the optical signal and, in one aspect of the invention, can be used to select or scan portions of the collected light pattern into an optical slit or aperture. In one aspect, the optical hub includes a filter mechanism capable of tracking movement of the fold mirror. In one aspect, the optical hub also controls positioning the collection mirror in proximity to the sample being analyzed.

Description

Cathodoluminescent optical concentrator

Cross Reference to Related Applications

This application claims priority to U.S. provisional patent application No.62/671152, filed on 2018, 5, month 14, the entire contents of which are hereby incorporated by reference.

Technical Field

When a sample is bombarded by high energy charged particles, such as an electron beam or an ion beam, photons can be emitted depending on the sample material. This phenomenon is called Cathodoluminescence (CL). The collection and detection of these photons in the wavelength range from Ultraviolet (UV) to visible to Infrared (IR) light can provide a great deal of information about the sample under investigation. The CL is typically examined in the electron microscope with respect to the sample and collected by directing photons to, for example, a photosensor, an imaging array, or a spectroscopic device, any or all of which may be located outside of the electron microscope beam column. The interior of the electron microscope beam column is maintained at a low pressure so electrons can travel to the sample without being significantly scattered by the gas in the beam column. After the light is collected, it can pass from the low pressure environment through the optical window and into an instrument that analyzes the CL light.

A common way of collecting photons emitted via CL is via a collecting mirror, which may be a parabolic mirror, located on an axis with respect to the electron beam (e-beam), and either above (more typically) or below the sample or both above and below the sample. In the case of a collection mirror located above the sample, on an axis with respect to the electron beam, the mirror will have a hole to allow the electron beam to pass through the mirror to the sample without obstruction.

The CL signal, which includes the emitted photons, contains a large amount of information about the sample from which the signal was emitted. Analysis of the CL signal can utilize total CL intensity, spectral information, polarization information, and angle-resolved light emission. The CL signal is often weak and it is often important to retain as much signal as possible for analysis. Furthermore, it is often important to have separate analysis optics and detectors, referred to herein as CL instruments, each optimized for a particular signal. For example, if spectral information is not important for analysis, it may be desirable to couple the collected light directly into the light sensor, rather than passing the light through the spectrometer (where some portion of the light is lost) and then into the light sensor.

Aligning the CL mirror on the sample so that the focal point of the CL mirror is precisely at the spot on the sample where the electron beam bombards and the CL is emitted can be a difficult and time consuming process. Thus, if multiple instruments are mounted on the microscope column and the CL-mirror is aligned for each instrument, it can be difficult to perform more than one type of analysis on the CL-light. Multiple instruments for CL analysis can be combined, allowing a user to use the same CL collection mirror without having to reposition relative to the sample for multiple measurements. However, one difficulty with combining multiple instruments is directing the collected CL light to different instruments with minimal loss of any information contained in the CL light, including, for example, CL intensity, spectral information, polarization information, and angle-resolved light emission.

Drawings

FIG. 1 is a diagram of an apparatus for collecting cathodoluminescent light in an electron microscope;

FIG. 2 is a schematic drawing of an exemplary CL optical system designed with an optical hub;

FIG. 3 is a schematic depiction of an exemplary CL optical system utilizing an optical hub design and three separate CL detection instruments;

FIG. 4 is a schematic depiction of an exemplary CL optical system designed with an optical hub equipped with a movable filter mechanism;

FIG. 5 is a schematic depiction of an exemplary CL optical system designed with an optical hub, equipped with a movable filter mechanism, and configured for fine position control of the optical hub fold mirror to select portions of an image pattern to pass through an optical aperture;

fig. 6 is an isometric depiction of an exemplary CL optical hub; and is

Fig. 7 illustrates internal components of an optical hub in accordance with an aspect of the present invention.

Detailed Description

Those skilled in the art will recognize other detailed designs and methods that can be developed using the teachings of the present invention. The exemplifications set out herein are illustrative and not limiting of the scope of the invention, as defined by the appended claims. The following detailed description refers to the accompanying drawings. The same reference numbers in different drawings may identify the same or similar elements.

In a typical CL instrument, as shown in fig. 1, an electron microscope 100 (not shown) generates an electron beam 10, the electron beam 10 exiting a pole piece 12 and being directed to a sample 30. At the point 32 where the electron beam 10 bombards the sample 30, Cathodoluminescent (CL) light 34 may be generated. A collection mirror 20, which may be a parabolic mirror, is provided to reflect the CL light 34 to a detector, which may be located outside the electron microscope 100. The collecting mirror 20 will typically have apertures 22 to allow the electron beam 10 to pass through, as the mirror 20 may be made of a material that would otherwise block the electron beam (e.g., diamond polished aluminum). When properly focused on the sample 30, the CL light 34 collected by the collection mirror 20 produces a light pattern 35, the light pattern 35 being collimated along the exit optical axis (not labeled) of the mirror 20. In a typical CL instrument, the light collected by the collection mirror 20 is sent to different CL analysis instruments using a series of fold mirrors and possibly optical switches to route the light pattern 35 to the individual instruments.

In one aspect of the invention, as shown in fig. 2, an "optical hub" 150 is configured to transmit light collected by the collection mirror 20 to a different CL analysis instrument (not shown). The optical hub 150 is connected to the electron microscope 100 via a port adjuster 140, which port adjuster 140 may also be configured to adjust the position of the optical axis 36 in a direction perpendicular to the optical axis 36. The interior of the optical hub 150 shares the same low-pressure environment as the interior of the electron microscope 100. The internal components of the optical hub 150 include materials that do not "contaminate" the environment of the electron microscope 100 and enable X-ray radiation generated within the electron microscope 100 to be safely contained within the electron microscope 100 and the optical hub 150. A linear actuator 160, which may comprise a motor-driven lead screw, moves the carriage 162 parallel to the optical axis 36 and causes the fold mirror 164 to intercept and redirect through the

optical windows

222, 224, 226 and the substantially collimated light pattern 35 outside of the low pressure environment of the electron microscope 100. An important advantage of this approach is that there is no fundamental limit on the number of optical windows supported, and the adjustable nature of the position of the fold mirror 164 via the mobile carriage 162 allows for fine alignment of the light pattern 35 into a CL instrument mounted outside of the optical windows (e.g., 222, 224, and 226). Furthermore, the optical hub 150 can be easily reconfigured with different CL instruments without having to change the optical hub (150) components. Further advantages of the optical hub solution are: fewer fold mirrors and optical switches may be required than in typical designs.

In a further aspect of the invention, as shown in fig. 2, a mechanism 172 is provided to support the collection mirror 20 above the sample 30. For optimum performance, the collection mirror 20 may be finely positioned such that the focal point of the collection mirror 20 coincides with the electron microscope 100 where the electron beam is focused on the specimen 30. It is also useful to be able to retract the collection mirror 20 a sufficient distance so that it does not interfere with the operation of the electron microscope 100 when CL photons are collected. Retraction and precise positioning can be achieved using a linear actuator 170, which linear actuator 170 may comprise a motor driven lead screw that moves a mechanism 172 parallel to optical axis 36. It may be desirable to coordinate the movement of the bracket 162 and the mechanism 172 to prevent collisions. For example, a controller (not shown) may control movement of the carriage 162 relative to the mechanism 172.

Fig. 3 shows an exemplary CL system having an optical hub 150 as described above, and three separate

CL detection instruments

232, 234, 236 mounted over optical hub

optical windows

222, 224, and 226 (not labeled in fig. 3). The position of the fold mirror 164 selects which instrument is capable of analyzing the light pattern 35. Examples of three

CL detection instruments

222, 224, and 226 that may be used are: (1) a spectrometer for measuring intensity and wavelength, (2) a photomultiplier tube (PMT) for measuring total intensity with high quantum efficiency, and (3) a camera for measuring and/or capturing the distribution of light in an image pattern.

In a further aspect of the invention, as shown in FIG. 4, an optical filter mechanism 229, which may include one or more optical filters or polarizers, can be moved to intercept the light pattern 35 after the optical pattern 35 is directed by the fold mirror 164, or can be moved out of the path of the optical pattern 35. The optical filter mechanism 229 is desirably capable of traveling along the axis 36 to any of the optical windows (e.g., 222, 224, and 226) and may be moved using the linear actuator 228. CL detection instruments (e.g., 222, 224, and 226) are mounted above the optical filter mechanism and are not shown in fig. 4. The filter mechanism 229 may comprise a plurality of filters arranged to be remotely selectable by a filter selection actuator.

In a further aspect of the invention, as shown in fig. 5, the optical aperture 250, which may be a slit or hole inside the CL detection instrument (e.g., one of the

instruments

222, 224, or 226), is configured to limit the portion of the light pattern 35 that is allowed to travel through the optical aperture 250. The adjustable nature of the position of the fold mirror 164 allows for fine positioning of the light pattern 35 onto the optical aperture 250 such that the portion of the light pattern 35 passing through the aperture 250 can be adjusted. This capability may optionally be combined with the use of the optical filter mechanism 229.

Fig. 6 is an isometric depiction of an optical hub 150 according to an aspect of the present invention. The optical hub 150 is mounted to an electron microscope (not shown) at a mounting flange 210 via a port adjuster 140. The optical hub 150 includes a collection mirror 20 and a mirror support mechanism 172.

Fig. 7 illustrates the internal components of an optical hub 150 in accordance with an aspect of the present invention. The mechanism 172 configured to support the collection mirror 20 is moved using a lead screw 272 and a motor 273. Fold mirror carriage assembly 162 (shown here without fold mirror 164 mounted for clarity) is moved via lead screw 262 and electric motor 263.

In further aspects of the invention, light may be introduced from outside the electron microscope 100 via the optical hub fold mirror 164 and into the sample 30 by way of the collection mirror 20 or from other sources within the electron microscope 100. In this aspect of the invention, collecting some of the light exiting the sample 30 by the collection mirror 20 may include: light emitted from active electronics, or reflected, fluoresced, scattered light incident on the sample 30 that is wavelength shifted from the light source.

Although the present invention has been described above in detail, it should be clearly understood that it is obvious to those skilled in the art that the present invention may be modified without departing from the spirit of the present invention. Various changes in form, design or arrangement may be made to the invention without departing from the spirit and scope of the invention. Accordingly, the foregoing description is to be considered exemplary rather than limiting, and the true scope of the invention is that defined by the following claims.

No element, act, or instruction used in the description of the present application should be construed as critical or essential to the invention unless explicitly described as such. Likewise, as used herein, the article "a" is intended to include one or more items. Further, the phrase "based on" is intended to mean "based, at least in part, on" unless explicitly stated otherwise.

Claims

1. An apparatus for collecting and analyzing light in an electron microscope, comprising:

a mechanism supporting a collection mirror at a distal end, the mechanism configured to extend into a sample chamber of the electron microscope and position the collection mirror proximate to a sample under analysis;

the collection mirror is configured such that light collected by the collection mirror forms a light pattern that is collimated along a linear axis, and light rays forming the light pattern are substantially parallel to each other;

a first linear actuator having a carriage supporting a fold mirror disposed to receive light directed by the collection mirror;

wherein the first linear actuator is configured to move the fold mirror to a plurality of fixed positions, each of the fixed positions being associated with a set of optics or detectors arranged to analyze the light.

2. The apparatus of claim 1, further comprising:

a movable optical filter assembly configured to move to the plurality of fixed positions in coordination with the fold mirror.

3. The apparatus of claim 1, further comprising: an optical aperture or slit located in a portion of a cathodoluminescence detection instrument, and wherein the fold mirror is configured to direct a portion of the light pattern through the aperture or slit.

4. The apparatus of claim 1, wherein the mechanism supporting a collection mirror comprises a second linear actuator configured to position or move the collection mirror to be adjusted above or below the sample under analysis.

5. The apparatus of claim 1, wherein the light collected by the collection mirror is cathodoluminescent light or other light exiting the sample, comprising: light emitted from active electronics, or reflected, fluoresced, scattered light incident on the sample that is wavelength shifted from the light source.

6. The device of claim 1, wherein the first linear actuator comprises a first lead screw and a first motor.

7. The apparatus of claim 4, wherein the second linear actuator includes a second lead screw and a second motor.

8. The apparatus of claim 2, further comprising:

a third linear actuator configured to position the movable optical filter assembly.

9. The apparatus of claim 2, wherein the movable optical filter assembly comprises: a plurality of optical filters; and an optical filter selection actuator configured to align one of the plurality of optical filters with the fold mirror.

10. The apparatus of claim 1, wherein the fold mirror is further configured to introduce light into the electron microscope.

11. The apparatus of claim 1, further comprising:

a port regulator configured to: the device is mounted to an electron microscope port and the position of the optical axis of the collected light is adjusted in one or more directions perpendicular to the optical axis.

12. The apparatus of claim 2, further comprising:

an optical aperture or slit located in a cathodoluminescence detection instrument, and wherein the fold mirror is configured to position a portion of the light pattern through the aperture or slit, and wherein an optical filter is positioned between the fold mirror and the optical aperture or slit.

13. The apparatus of claim 1, wherein the mechanism supporting a collection mirror at a distal end, the first linear actuator having a carriage supporting a fold mirror, and the fold mirror are all located within a low pressure chamber comprising part of the electron microscope.

14. The apparatus of claim 4, wherein the mechanism supporting a collection mirror at a distal end, the first linear actuator having a bracket supporting a fold mirror, the fold mirror, and the second linear actuator are all located within a vacuum chamber comprising part of the electron microscope.